The present invention relates generally to a high speed printer primarily for use on mini computer units, and more particularly it relates to the matrix-type impact printer utilizing a plurality of print wires which are selectively propelled at their input ends to cause their other end to impact a recording medium and to print a dot thereon. A series of these dots printed by the wires forms a character.
In the matrix printer art, it is desirable to have the input ends of the styli or print wires to be configured as close together as possible just as they are configured in a continuous linear array at the output impact end. This will minimize the deflection of the wire paths from their input to their output ends. However, for various reasons to be explained below, it has been found that a non-spreading linear pattern configuration at the input end of the print wires is difficult to achieve due to the physical size limitation of the various components. To have the print wires configured in a minimal spreading pattern at their input ends would produce a desirable substantially straight wire path and hence result in less friction and wear being applied to the wires at the support points than would be the case where the input ends of the wires are configured in a spreading pattern which results in severely curved wire paths. The magnitude of the frictional force and wear at the wire supports is in direct proportion to the degree of severity of the wire path curvature.
One reason for the difficulty to have the print wires to be configured in a extremely close pattern at their input end is because of the need for the physical size of the tips of wires at the input end where the wires are contacted by a stylus-propeller to cause the necessary impact by the wire on the recording medium. That is, the input end of the print wire needs to have a head of some dimension to allow for the necessary contact between the stylus or print wire and the stylus propeller which needs also to have some dimension in order to make the necessary contact with the head of the print wires. Therefore, the input head of the print wire and also the tip of the means which propells the print wire must be of some dimension at the input end of the wire. This is necessary since if the stylus head was but a point which was of no greater dimension than the remaining body of the stylus or print wire and if the stylus propeller was of no greater dimension than the remaining body of the stylus, contact between the two small points would be very difficult to maintain without physically bonding the two together, which may then create manufacturing cost and other disadvantages such as degraded performance.
Another reason why a spreading configuration of the styli at the input ends is necessary, is because of the physical size and location of the coil of wire which is wrapped around one of the magnetic poles of the electromagnetic actuators which powers the stylus-propeller to propell the styli to impact the recording medium. It is common knowledge that the larger the number of turns in the coil of wire which is wrapped about the magnetic pole, the stronger the force which is produced by the pole. Therefore, where a large number of turns of wire is wrapped around the pole at the input end of the styli, a greater space is needed to situate the poles than where a smaller number of turns of wire is used. However, there is also a need to minimize the length of the stylus propeller in order for them to be as light as possible. Therefore, the contradictory requirements of a large coil v. a short stylus propeller necessitates some degree of spreading of the styli at the input end.
It therefore follows that an objective in the matrix print head art is to maintain the input end of the styli or print wires in a minimal spreading configuration given the coil size and stylus propeller length constraints, in order to minimize the friction applied to the wires at the supports and, as such, to minimize the wear on the wires. Several prior art apparatuses have attempted to accomplish this end. For example, in U.S. Pat. No. 3,994,381, a print head is disclosed which has the input end of the print wires configured in an elliptical configuration. Such a configuration has the effect of bending all print wires at their input end by the same amount. That is, while the print wires of the U.S. Pat. No. 3,994,381 are not configured in a continuous linear array at their input end, resulting in no bend in the wires at this end and, as such, minimal friction applied to the wires, all wires are bent by the same amount, with all bends being equally shallow or equally deep. In such a configuration, none of the print wires are favored, with less bend, any more than any of the others. That is, all wires are favored or none are favored. In the U.S. Pat. No. 3,994,381, where one print wire may be used during printing more than any of the other print wires to make characters, it follows that this most frequently used wire will get more wear and, as such, would likewise have a shorter life span than the other wires, because it is bent just as much at the input end as the wires which are less frequently used.
U.S. Pat. No. 3,929,214 teaches a print head which has the input end of the styli configured in a circle. In such a configuration, some of the print wires at their input ends are bent more than other wires in the configuration in order to be propelled by a stylus propelling means. While some of the wires in the circular configuration are bent more than other wires in a circle, some of these wires would also be bent more than some of the wires in the elliptical configuration of the U.S. Pat. No. 3,994,381 given similar physical size constraints. Also, some wires in the circular configuration are bent less at their input end than other wires in the circular configuration and would also be bent less than some of the wires in the elliptical configuration of the U.S. Pat. No. 3,994,381 given similar physical size constraints. It follows that in the configuration of the U.S. Pat. No. 3,929,214 some wires are favored with less bend, but it is not necessarily the wires which are most frequently used during the printing of characters. That is, there is no advantageous relationship between the wires which are bent the least in the circular configuration and the frequency of use of such wires.
Because of the above discussed problems still remaining in the prior art where the input end of the printing wires are configured in other than a continuous linear array, it follows that it is desirable to have the input ends of these print styli configured at their input end such that those print wires which are most frequently propelled to form characters on a recording medium have the least curvature of their paths so as to result in less wear on these frequently used wires and, as such, to allow for a longer life span for these wires.
Another problem which several prior art print heads have been confronted with is that of adjusting or controlling the air gaps between the stylus-propelling means and the magnetic pole or actuators in order to obtain the desired propelling force on the styli. That is, where a propeller armature, attracted by a magnetic pole, is used to propell the styli, the area between the armature tip which contacts the styli head and the attracting pole which attracts the armature toward it must be controlled or maintained within a range such that the pole will attract the armature tip with a force sufficient to propell the styli through the stylus guide assembly to impact the recording medium. It is desirable that all air gaps for all actuator-stylus propeller combinations in the same print head, as well as all combinations for all print heads manufactured with the same design, be substantially uniform.
Several prior art print heads have incorporated means for adjusting or attempting to control the air gaps in the above combinations, but all efforts so far have met with certain undesirable results. For example, the U.S. Pat. No. 3,994,381, which made use of nine print styli, nine different stylus propelling means and nine different actuators, have also incorporated nine separate and distinct adjustment means to adjust or control the air gaps between the various stylus-propellers and their respective actuators. While such separate means of adjusting the individual air gaps may prove to be quite accurate or efficient, it is undesirable because it is time-consuming and results in greater expense to manufacture.
The '241 patent has sought to deal with the problem of adjusting the air gaps by incorporating one central adjuster for all nine of its stylus propeller-actuator units. Such a central adjusting system obviously has the undesirable result of not being very effective, especially for non-circular pole patterns, where stresses can and usually are introduced into the system and result in the uneven settings of air gaps of the stylus propeller-actuator combinations.
It therefore follows that there is a need in the matrix print head art for a print head apparatus which either has a more efficient and economical means of adjusting the stylus propeller-actuator combination or an apparatus which eliminates the need for adjusting the combinations altogether.
An additional problem which is still present in the prior art print heads is that of adequately and economically supporting the print wires in a bearing assembly at their input ends where they are configured in a spreading pattern configuration. That is, where the print wires are configured at their input ends in a spreading pattern, they must be supported in an angular or slanted position near their input ends and be straightened out near their output or impact ends to form a continuous linear array at their impact ends. In most of the matrix impact printers of the type herein described, a stylus guide means has been incorporated with an initial sytlus bearing support member at the input end of the styli which has been provided with as many apertures, configured about its periphery, as there are styli. The apertures, in order to provide full wear support, need to be formed through the bearing in a slanted direction to support the styli at its input end at an angle relative to the bearing member. In the prior art print heads where there have been seven or nine different styli used to provide long wear, it would have been necessary to form seven or nine apertures in seven or nine different angular directions in the bearing support member. This would result in great expense and hence are not done, thereby penalizing the wear characteristics.
It therefore follows that it is desirable to have an improved bearing support member suitable for supporting the styli in the necessary slanted position at their input ends where all apertures in the support member may be formed at the same angles. That is, it would be highly desirable to have a bearing support member with apertures which simulate a long single slanted aperture, but which is far more economical to manufacture than a bearing where a single slanted aperture must be formed through a rather thick support bearing.